1. Field of the Invention
The present invention relates to display apparatuses in which electroluminescent (EL) devices that emit light depending on an input current are arranged in a matrix and to methods for driving the display apparatuses. More specifically, the present invention relates to an active-matrix display apparatus including current-driven light-emitting devices and current-programmed pixel circuits and to a current supplying method for the display apparatus.
2. Description of the Related Art
Recently, self-illuminating displays including light-emitting devices have attracted attention as next-generation displays. In particular, organic EL devices, which are current-controlled light-emitting devices whose illumination brightness is controlled by a current flowing in the devices, have been extensively applied and developed.
In color organic EL displays, a set of light-emitting devices of three primary colors of red (R), green (G), and blue (B) that are disposed side by side is used as a unit to display one color, and such light-emitting devices are arranged in rows and columns to form a matrix display apparatus. The light-emitting device of each of RGB colors is made of an EL material that emits light having a wavelength of the corresponding color.
There are variations in illumination brightness between the respective colors even when the same current flows. In organic EL materials available for practical use, a light-emitting material for blue (B) exhibits a lower current-luminance efficiency characteristic than that for red (R) and green (G). The current-luminance efficiency is defined as the ratio of the current per unit area (A/m2) to the luminance (cd/m2).
In organic EL panels, a large amount of current is supplied to light-emitting devices having a low current-luminance efficiency to obtain an RGB-balanced illumination brightness. It is therefore attempted to increase the amplitude of input image signals of the low-current-luminance-efficiency light-emitting devices compared with the light-emitting devices of the remaining colors or to increase the voltage-current conversion gain of a current-data generation circuit only for the low-current-luminance-efficiency light-emitting devices so that a large amount of current can flow in the pixels of the corresponding color.
However, if uniform brightness is achieved by correcting the amplitude of the input image signals, the amplitude will be largely corrected to significantly increase the signal voltage of the specific color, and the power supply voltage of a modifying circuit needs to increase correspondingly, which is undesirable. In view of a low power supply voltage required for the power supply of a controller IC that controls the amplitude of the input image signals, it is difficult to increase the amplitude of the input image signals.
Further, if the voltage-current conversion gain of the current-data generation circuit is increased for a specific color, there is no compatibility between current generation circuits of different colors. Thus, the pattern of the current generation circuits needs to be changed for a different color arrangement of a display section.